1. Field of the Invention
The invention pertains to a fabricating method of a thin film pattern of a display panel, and more particularly to a reverse resist printing device and a fabricating method of a thin film pattern using the same.
2. Description of the Related Art
Recently, various flat panel display devices, which can reduce the weight and size that are a disadvantage of a cathode ray tube, have been on the rise. The flat panel display devices includes liquid crystal displays, field emission displays, plasma display panels, organic electro luminescence (hereinafter, referred to as ‘EL’) displays, etc.
Among these, the liquid crystal display devices control the light transmittance of liquid crystal by using an electric field, thereby displaying a picture. To this end, a liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in a matrix shape, and a drive circuit for driving the liquid crystal display panel.
The liquid crystal display panel includes a thin film transistor array substrate and a color filter array substrate that face each other; a spacer for keeping a fixed cell gap between the two substrates; and a liquid crystal filled in the cell gap.
A thin film transistor array substrate includes gate lines and data lines, a thin film transistor formed as a switch device at each of the crossing parts of the gate lines and the data lines; a pixel electrode formed by the unit of a liquid crystal cell to be connected to the thin film transistor; and an alignment film spread thereon. The gate lines and the data lines receive signals from drive circuits through pads, respectively. The thin film transistor supplies a pixel signal supplied to the data line to a pixel electrode in response to a scan signal supplied to the gate line.
A color filter array substrate includes color filters formed by the unit of a liquid crystal cell; a black matrix for dividing the color filters and reflecting an external light; a common electrode for commonly supplying a reference voltage to the liquid crystal cells; and an alignment film spread thereon.
Separately making the thin film transistor array substrate and the color filter array substrate and bonding them together complete the liquid crystal display panel. Then, a liquid crystal is injected and the panel is sealed.
A photolithography process and an etching process form the thin film patterns within the related art liquid crystal display panel.
However, the photolithography process includes a number of processes such as an exposure process, a development process, a cleaning process, an inspection process, etc, thereby causing an increase of the manufacturing cost of the liquid crystal display panel. Accordingly, a method of patterning a thin film by a reverse resist printing method is used instead of the photolithography process.
FIG. 1 shows a diagram representing a reverse resist printing device.
The reverse resist printing device shown in FIG. 1 includes a print roller device 10 having a roll shape where a blanket 15 composed of polydimethylsiloxane (PDMS) is wound. An etch resist solution spray device 12 sprays an etch resist resin solution, and an engraved print plate 20 includes a groove 20A, which has the same shape as a thin film pattern that is to be formed, and a projected part 20B which borders the groove 20A.
FIGS. 2A to 2E are diagrams that explain the forming of a thin film pattern by the reverse resist printing device of FIG. 1. Especially, FIGS. 2A to 2D represent a forming process of a gate pattern of the liquid crystal display panel by using the reverse resist printing method.
First, as shown in FIG. 2A, an etch resist solution 14A from the etch resist solution spray device 12 is sprayed onto the blanket 15 that is wound around the print roller device 10. The print roller device 10 rotates to coat the blanket 15 with the etch resist solution 14A.
Then, as shown in FIG. 2B, the etch resist solution 14A transfers only to the projected part 20B in the print roller device 10 as the print roller device 10 coated with the etch resist 14A simultaneously rotates and contacts the print plate 20. Accordingly, as shown in FIG. 2C, an etch resist solution 14B having a desired thin film pattern shape remains on the print roller device 10.
Then, as shown in FIG. 2D, the etch resist solution 14B, which was transferred to the print roller device 10, transfers again onto a substrate 30 where a designated metal layer, e.g., a gate metal layer, is formed. Then, the resist is cured. Accordingly, as shown in FIG. 2E, the etch resist pattern 14C for patterning the metal layer 32A can be formed. Afterwards, the metal layer 32A not overlapping the etch resist pattern 14C is patterned, thereby forming the desired thin film pattern on the substrate 30. Here, if forming the gate pattern such as the gate line, the gate electrode, etc. of the liquid crystal display panel, the gate pattern can be formed using chromium (Cr), aluminum neodymium (AlNd), etc. as the metal layer 32A.
The etch resist solution 14A used in the reverse resist printing device is formed of a basic polymer such as novolac, etc. a carrier solvent, a printing solvent, a surfactant, etc.
Here, the carrier solvent is a solvent that reduces the viscosity of the etch resist solution 14A sprayed from the etch resist solution spray device 12 so that the etch resist solution 14A can be evenly coated over the blanket 15.
The printing solvent is used for the etch resist solution 14A coated on the blanket 15 to impart a tack characteristic or adhesiveness.
The surfactant is a material which is applied to an interface to greatly decrease the surface tension of the interface and which acts to decrease the surface tension of the etch resist solution 14A. If a silicon-based surfactant is used, the coating can be good but the silicon-based material contaminates the blanket. Thus, a fluorine-based surfactant is used. However, the fluorine-based surfactant reduces the surface energy of the etch resist solution 14A, thus the adhesive force between the etch resist solution 14A and the blanket 15 becomes similar to the adhesive force between the etch resist solution 14A and the print plate 20. As a result, the characteristic that the etch resist solution 14A is transferred from the blanket 15 to the print plate 20 decreases, and thus the reliability of forming the thin film pattern by the resist printing method deteriorates.